In an image forming device such as a laser printer and a digital copier, a laser beam scans a photosensitive body in correspondence with data of an image to be printed. Thereby an electrostatic latent image is formed on the photosensitive body. Then, the image forming device forms an image by supplying developer to the electrostatic latent image, transferring the image to a recording sheet and fixing the image on the sheet.
The image forming device is required to be downsized and low-priced in recent years. In accordance therewith, a light source device that irradiates the laser beam for forming the electrostatic latent image is also required to have a small size and a simple structure, while high accuracy in a product is also required.
The light source device includes a semiconductor laser and a coupling lens (or also called a collimating lens) that gathers the laser light emitted from the semiconductor laser and converts the laser light to a light flux. These two members are positioned with their optical axes being aligned with each other with high accuracy.
Japanese Patent Application Laid-Open Publication No. Hei-11-231237 (which will be referred to as Document 1 hereinafter) discloses, in its FIG. 1, a light source device in which a laser holder that holds a semiconductor laser and a lens holder that holds a coupling lens are prepared separately. The semiconductor laser and the coupling lens are fixed on the respective holders, and the holders are fixed after being positioned corresponding to each other. The lens holder is formed in a cylindrical shape so as to surround the whole circumference of the lens.
Japanese Patent Application Laid-Open Publication No. 2002-31773 (which will be referred to as Document 2 hereinafter) discloses, in its FIG. 2, another light source device that has a more simplified configuration in comparison with the configuration described above. The light source device described in Document 2 uses a holder (holding member) that is formed by integrating a part (main part) for holding the semiconductor laser and a part for holding the coupling lens. The part for holding the coupling lens is in a base shape that protrudes from the main part of the holder in front thereof. After the semiconductor laser is fixed on the holder, the coupling lens is fixed with photopolymerizable or light-curing resin on the base portion of the holder in front of the semi-conductor laser. It is noted that the photopolymerizable resin is provided not only between the coupling lens and the base, but also a part of the photopolymerizable resin protrudes outside from between the coupling lens and the base both on the front and rear sides of the coupling lens. Japanese Patent Application Laid-Open Publication No. Hei-9-218368 (which will be referred to as Document 3 hereinafter) discloses, in its FIG. 1, a case where the photopolymerizable resin is provided only between the coupling lens and the base.